The present invention relates to a ramjet for a supersonic and hypersonic aircraft, intended to operate over a wide range of speeds, especially between Mach 2 and Mach 8.
The design of such a ramjet, generally called compound ramjet because it possesses an extended operating domain, by virtue of the succession of a subsonic combustion phase and of a supersonic combustion phase, raises numerous difficulties both as regards the definition of the aerodynamic stream as well as the production of the structure delimiting this stream.
Various techniques have been employed in order to attempt to overcome these difficulties. Among these techniques, one of the most interesting is that described by the document U.S. Pat. No. 5,727,382.
This document describes a ramjet including an elongate ramjet body which consists of four walls opposite in pairs, which between them delimit:
an inlet for a flow of oxidant,
a variable-geometry combustion chamber, which is provided with at least one fuel injector and in which the oxidant/fuel mixing and the combustion of said mixture are carried out, and
an exhaust nozzle, channeling the gases leaving said combustion chamber,
two of said opposite walls being flat and parallel to each other.
In this known ramjet, one of the other two opposite walls is produced by the use of plates which are articulated one after the other, so as to be deformable. A system of actuators makes it possible to set up and maintain said deformable wall in the geometry desired as a function of the conditions of flight. The advantage of such a controlled deformable wall lies in the capability of precisely adapting the progressive changes in the cross section of the combustion chamber along the length of the chamber to each flight condition, and in the possibility of putting in place a geometric-nozzle neck suitable for subsonic combustion. On the other hand, the practical production of such a ramjet is complex and expensive, especially because of the changes between moving plates. Moreover, in order to be able to form a satisfactory subsonic combustion chamber, this ramjet has to include a supersonic combustion chamber which is a little too long, which to a degree limits the performance of said ramjet at high speed and complicates its cooling.
Furthermore, the document GB-2 222 635 describes a ramjet for a supersonic and hypersonic aircraft, including an elongate body which consists of:
two sidewalls, flat and parallel to each other;
a fixed upper wall, integral with said sidewalls and exhibiting, in profile, the rigid general shape of a V open at an obtuse angle, in such a way that said upper wall includes a front flank and a rear flank which are inclined with respect to one another and linked by a ridge which is at least approximately orthogonal to said sidewalls; and
a lower wall mounted movably as one between said sidewalls so as to be able to slide longitudinally in translation, said lower wall also featuring, in profile, the rigid general shape of a V open at an obtuse angle, but reversed with respect to that of said upper wall, said lower wall thus including a front flank and a rear flank which are inclined with respect to one another and linked by a ridge at least approximately orthogonal to said sidewalls,
said walls of said body delimiting between them:
an inlet for a flow of oxidant;
a combustion chamber, which is provided with at least one fuel injector and in which the oxidant/fuel mixing and the combustion of said mixture are carried out; and
an exhaust nozzle, channeling the gases leaving said combustion chamber and formed between said rear flank of the upper wall and the rear flank of the lower wall.
In this latter document, the sliding lower wall acts as a shock diffuser.
The object of the present invention is such a ramjet with sliding lower wall making it possible to obtain an optimal combustion chamber, whether the combustion is subsonic or supersonic.
To that end, according to the invention, the ramjet with sliding lower wall, of the type reiterated above, is noteworthy in that:
said fuel injector is arranged in the vicinity of the ridge of said upper wall;
said front flank of the lower wall includes:
at least one first face, in a general direction at least substantially parallel to the rear flank of said upper wall and arranged facing said rear flank of said upper wall; and
at least one second face, linked securely to said first face along a joint line at least approximately orthogonal to said sidewalls, said second face being inclined with respect to said first face in such a way that, facing said upper wall, the assembly of said first face and of said second face is concave;
said ridge of the upper wall faces said second face of said lower wall, while said joint line between said first and second faces lies opposite the rear flank of the upper wall, such that said second face is arranged with regard to said fuel injector with a part facing the rear flank of the upper wall and a part facing the front flank of said upper wall;
said combustion chamber is formed between, on the one hand, said rear flank of said upper wall and, on the other hand, said first face and the corresponding part of said second face of said lower wall;
said oxidant inlet is formed between the front flank of said upper wall and the corresponding part of said second face of said lower wall; and
the sliding of the lower wall brings said joint line between said first and second faces closer to said fuel injector so as progressively to modify the geometries of said oxidant inlet and of said combustion chamber, said geometries passing progressively from a first state in which, for a Mach number lying between 1.5 and 3, said oxidant inlet constricts said oxidant flow only slightly and said combustion chamber is long and divergent, to a second state in which, for a Mach number lying between 8 and 12, said oxidant inlet strongly constricts said oxidant flow and said combustion chamber is shorter and exhibits a constant cross section.
Hence, by virtue of the present invention, by simply employing the linear or curvilinear translation of one of the walls of the ramjet, the progressive variation in the cross section of the combustion chamber and of the geometries of the oxidant inlet and of the nozzle are obtained, which makes it possible to match the ramjet to the conditions of flight of the aircraft, so as to obtain the maximum performance from it as regards either the thrust, or the specific impulse. To do this, the two walls of the ramjet, other than the two which are flat and parallel to each other, are profiled in such a way that said translation leads to very different cross section laws being imposed; an oxidant (air) inlet with a low degree of constriction associated with a long and divergent combustion chamber equipped with a geometric-nozzle neck for the low Mach numbers, and an air inlet with a high degree of constriction associated with a shorter combustion chamber with constant cross section for the high Mach numbers.
The implementation of the present invention therefore makes it possible to dispense with the variable-geometry wall of the ramjet of the document U.S. Pat. No. 5,727,382, with its drawbacks which are the hinges for articulation of the plates, the plurality of actuators for these plates, etc. In contrast, in the ramjet of the invention, a single actuator is necessary in order to achieve said translation. Furthermore, it is possible to accept an incomplete leaktightness of said wall which is movable in translation with said flat and parallel walls.
Said movable second wall is preferably shorter than said first upper wall.
Furthermore, in order to form, with said second face, a marked inlet neck (minimum cross section) for the oxidant flow, the ridge of said first wall exhibits the shape of a bevel.